1. Field of the Invention
The present invention relates to a composition which is constantly unsusceptible to damages due to light, heat and/or oxygen, or to a composition which is useful for preparing color filters used for an LCD (liquid crystal display) and the like, and to an image forming method. More particularly, the present invention relates to a novel UV absorbent and a preparation method of the UV absorbent, and a composition containing therein the UV absorbent and an image forming method using the composition.
2. Description of the Related Art
Ordinarily, color filters to be used in a full-color LCD comprise pattern pixels having shieldability among red (R), green (G), and blue (B) pixels, respectively, in order to prevent light leakage and increase image contrast. The pattern pixels having the shieldability are formed by using a material in which a black colorant or the like is dispersed in a metallic film such as chromium or a photosensitive resin. However, in the case of the metallic film such as chromium or the like, pattern pixels are formed such that a metallic film is formed so as to cover the entire surface of a glass substrate by means of a deposition. Resist is coated on the substrate to pattern the substrate. Then, the metallic film is etched. Accordingly, processes with this method become very complicated, a yield is deteriorated thereby causing a problem with a manufacturing cost.
In order to solve the above-described problem, a method has been known in which a photosensitive black resin that is a combination of a photosensitive resin and a carbon or the like is used to form the pattern pixels having shieldability. With this method, a film thickness must have several xcexcm in order to have the film exhibit shieldability to a certain degree. However, ordinarily, when color filters are produced, due to problems of alignment errors, pattern pixels having shieldability and R, G, and B pixels must overlap to a certain extent, and it is thus unavoidable that irregularities are produced on a surface of a color filter. Therefore, in the present situation, in order to secure a surface whose smoothness is excellent, a smoothing layer is further formed on the surface, or a surface grinding is applied to the surface.
As a method of increasing smoothness of a color filter surface, Japanese Patent Application Laid-Open (JP-A) Nos. 3-209203 and 4-69602 disclose a so-called self-alignment method. In the self-alignment method, after the formation of R, G, and B pixels, a black photosensitive resin layer is applied onto the entire surface of a substrate, the substrate is exposed to light from the rear surface thereof, the R, G and B pixels themselves are used as exposure masks, whereby pattern pixels having shieldability are formed at gaps among the pixels. However, in each of R, G, and B colorants to be generally used, transmittance of each colorant in a UV region in which a black photosensitive resin composition is cured is high. Therefore, a problem has been caused in that the UV light transmits to a photosensitive resin composition provided on the R, G and B pixels, whereby even the photosensitive resin composition is partially cured and left on a portion of the pixels.
In order to solve the problem, JP-A Nos. 62-254103, 62-9301, 1-145626, and 2-77014 each discloses a method of adding or immersing a UV light absorbent in a composition. Further, JP-A No. 9-25360 discloses a method in which a UV absorbent precursor is used in view of preventing the occurrence of exposure energy deterioration or insufficient exposure that does not reach a film deep portion which is caused by the addition of the UV absorbent or the like. Namely, with the use of the UV absorbent precursor, imagewisely irradiated exposure energy is not blocked by the UV absorbent before the energy is transmitted to the film deep portion, whereby damages caused to R, G, and B pixel portions can be prevented.
If the photosensitive resin composition contains therein the UV absorbent precursor, generally, such a compound as disclosed in JP-A No. 9-25360 which has a triazine skeleton structure and which is symmetrically structured has been used as the UV absorbent precursor. However, the compound easily produces crystalline over time especially in an atmosphere of high temperature. For this reason, during the storage of the UV absorbent precursor, the compound may produce crystallization in the photosensitive resin composition thereby causing a defect of color unevenness to a finish product such as a color filter that has been formed by using the photosensitive resin composition. As a result, there has been caused a problem in that high quality product cannot be manufactured constantly.
JP-A No. 8-225679 also discloses the UV absorbent precursor having the tiazine skeleton structure. However, not a few problems have been caused in that insufficient solubility is often seen in exemplified compounds thereof, and if solubility is imparted to a precursor compound, more reaction time is needed for the preparation of the compound.
As described above, when the UV absorbent precursor whose absorptance of exposure energy is small is used, a composition using a triazine type UV absorbent precursor, which does not easily produce crystallization even in an atmosphere of high temperature, is not yet actually provided. Further, compositions using the UV absorbent precursors which are added for constantly preventing damage due to light, heat, and/or oxygen are desired not to easily produce crystallization.
In order to prepare the UV absorbent precursor, the UV absorbent that is to be a raw material for the precursor must be prepared in advance. Namely, in order to prepare the UV absorbent precursor, another process is required, thus making it possible to increase the manufacturing cost of the UV absorbent precursor.
Research Disclosure 433007 discloses a triazine type UV absorbent which has one OH group and in which the remaining five OH groups are entirely substituted. In the description of Research Disclosure 433007, a description has been made in which the remaining five OH groups may be substituted by an alkenyl group having 2 to 50 carbon atoms. However, neither a description has been made in which the alkenyl group is particularly preferable as a substituent nor a description has been made in which the remaining five OH groups are preferable to be substituted by the same alkenyl group. Therefore, the Research Disclosure 433007 is not directed to the characteristics of the alkenyl group and does not take a preparation method of such a UV absorbent into consideration.
In order to solve the above-described various conventional problems, the objects described below will be accomplished:
A first aspect of the present invention is to provide an improved UV absorbent which can be used as the UV absorbent precursor, whose maximum absorption is within a range of short wave, which has an alkenyl ether group as a protective group which can be de-protective when heated, and which has low crystallizability.
A second aspect of the present invention is to provide a method in which a UV absorbent is manufactured inexpensively during less processes.
A third aspect of the present invention is to provide a composition containing therein a UV absorbent which does not cause any image defect due to crystallization of the UV absorbent even in an atmosphere of high temperature and which is also excellent in storage stability.
A fourth aspect of the present invention is to provide an image forming method capable of forming images due to heat and constantly forming images without defects such as color unevenness and the like by using a recording material containing therein a UV absorbent.
Means for solving the above-described problems are described below:
A first aspect of the present invention is a UV absorbent represented by the following formula (1): 
wherein R1 represents an alkenyl group, each R1 represents the same group, and R2, R3 and R4 independently represent a hydrogen atom, an alkyl group, an alkoxy group, or a halogen atom.
A second aspect of the present invention is an image forming method comprising the steps of:
a) preparing a composition containing therein a UV absorbent represented by the following formula (1): 
xe2x80x83wherein, in formula (1), R1 represents an alkenyl group, each R1 represents the same group, and R2, R1 and R4 independently represent a hydrogen atom, an alkyl group, an alkoxy group, or a halogen atom;
b) applying the composition onto a substrate;
c) exposing the composition on the substrate; removing unnecessary portions of the compositions by development and forming pixels on the substrate; and
d) heating the pixels.
A third aspect of the present invention of a method of preparing a UV absorbent represented by the following formula (1) is produced by a reaction between a compound represented by the following formula (2) and an alkenylating agent represented by the following formula (3) in the presence of a base: 
wherein, in formula (1), R1 represents an alkenyl group, each R1 represents the same group, R2, R3 and R4 independently represent a hydrogen atom, an alkyl group, an alkoxy group, or a halogen atom; in formula (2), R2, R3 and R4 independently represent a hydrogen atom, an alkyl group, an alkoxy group, or a halogen atom; and in formula (3), X represents a halogen atom, xe2x80x94OSO2R5, or xe2x80x94OSO2OR1, and R5represents an alkyl group or an aryl group.